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MHT CET 2023 (13 May, Shift 2) · Photoelectric Effect: Einstein's Equation

Photoelectric Effect: Einstein's Equation question from MHT CET 2023 (13 May, Shift 2)

Q79MHT CET 2023 · 13 MAY · SHIFT 2Medium

Photoelectric Effect: Einstein's Equation

When radiations of wavelength $\lambda$ is incident on a metallic surface the stopping potential required is $4.8\text{ V}$ . If same surface is illuminated with radiations of double the wavelength, then required stopping potential becomes $1.6\text{ V}$ , then the value of threshold wavelength for the surface is

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Answer: (b)

In eV: $\frac{hc}{\lambda} - \phi = 4.8$ and $\frac{hc}{2\lambda} - \phi = 1.6$
Subtract: $\frac{hc}{2\lambda} = 3.2$ , so $\frac{hc}{\lambda} = 6.4$ eV and $\phi = 1.6$ eV
$\lambda_0 = \frac{hc}{\phi} = \frac{6.4}{1.6}\lambda = 4\lambda$
So the answer is (b) $4\lambda$ .

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